Geometry and electronic band structure of surfaces: the case of Ge(111): Sn and C(111)

We present an ab initio study of two semiconductor surfaces, the alpha phase of Sn on Ge(111) and the cleavage surface of diamond. The theoretical tools used (density functional theory (DFT) and many-body perturbation theory) are discussed in detail, and the advantages and disadvantages of the two approaches are pointed out. We show that in the case of diamond it is essential to go beyond the DFT single-particle approach, and to introduce quasiparticle effects through the GW approximation.